Even with the Kyoto Protocol due to expire at the end of this year, Obama persists in giving highest priority to climate change policy if re-elected. Does the U.S. really want to lead the world in committing economic suicide? It pays to look at the rapidly disappearing scientific rationale for trying to mitigate a putative future global warming.

In an essay Why the Global Warming Skeptics are Wrong in the New York Review of Books of Feb. 22, 2012, Yale professor William D. Nordhaus attempts to counter the arguments of a group of 16 prominent scientists who published an essay, No Need to Panic about Global Warming in the Wall Street Journal on Jan. 27, 2012.

Two crucial points may have been overlooked in the debate:

Evidence for anthropogenic global warming (AGW) is problematic.

A modest warming is likely to be beneficialnot damaging.

First, some background: I have known Bill Nordhaus for about 40 years; he certainly is no wild-eyed alarmist, but rather a highly respected specialist in environmental economics. Through his association with the U.N. climate-science panel, he is familiar with the main arguments supporting the IPCCs contention that human activities, mainly rising carbon dioxide levels from energy generation, have been responsible for much of past warming. He does not question this IPCC claim; however, I have no reason to believe that he supports any of the drastic CO2-mitigation schemesbe they carbon sequestration or alternative green energy projectsor that he has illusions about the efficacy of the Kyoto Protocol or similar measures of international control.

So I will simply try to address questions Prof. Nordhaus posed in his NYRB essay, to which I responded in a (Aug. 16) letter in the NYRB. I wanted my response to reach NYRB readers, typically liberal academics, lawyers, and teachers.

1. Is the planet in fact warming? This crucial question cannot be answered honestly unless one specifies the time interval referred to. Clearly, the climate has warmed since the last Ice Age. It has also warmed since about 1850, in recovering from the Little Ice Age (roughly 1400-1800 AD). But is has not warmed since the Medieval Warm Period of 1,000 years ago, or since the Holocene Optimum, which reached even higher temperatures 5,000-8,000 years ago. Nor has it warmed during the past decade.

Coming closer to the present, we see a warming between 1910 and 1940, which is real but not caused by human activities. Most would agree that the Earths surface cooled slightly between 1940 and 1975even though carbon dioxide, a greenhouse (GH) gas, had been steadily increasing during this period. Temperature data show a sudden, unexplained jump around 1976-1977. Surface weather stations then report a modest increase in temperature up to the year 2000although different analyses disagree on details and have been frequently revised. Many people, including Nordhaus, tend to identify this reported increase as caused by the almost parallel increase in CO2. In its Summary, the latest IPCC report (2007) states explicitly that this reported (surface) warming trend is sure (>90%) evidence for anthropogenic global warming (AGW).

We note, however, that the atmosphere, both over land and ocean, did not warm during this same post-1978 periodeven though atmospheric theory and every climate model predicts that the tropical atmosphere should warm nearly twice as rapidly as the surface. This atmospheric evidence comes from instruments in weather satellites, producing the only truly global dataand, independently, from thermometers in balloon-borne radiosondes.

In 2000, the U.S. National Academy of Sciences assembled a team of distinguished scientists to discuss the puzzle of surface warming in the absence of an atmospheric warming trend. However, their report, Reconciling observations of global temperature change, could not reconcile the disparity.

I note that an analysis of ocean data has shown no significant warming during the period of 1978 -2000. Independent non-thermometer data (so-called proxies, like tree rings, ice cores, ocean sediments, stalagmites, etc.) also show no warming trend between 1978 and 2000. Significantly, there has been no warming for the past decade. All this, in spite of constantly rising CO2 levels.

The inescapable conclusionor perhaps I should say suspicionis that land-based weather stations may be reporting just local temperature increases but that there is negligible global warming. If correct, this surmise would remove the main evidence for the IPCCs claim about the existence of appreciable AGW.

2. Are human influences an important contributor to warming? Obviously, the answer must be noif one accepts the evidence about the nonexistence of recent warming. Nevertheless, it should be stated that since CO2 is a GH, and since most if not all of its increase is human-caused, there must be some minor human contribution to climate change. The real scientific puzzle, not mentioned by Nordhaus, is why the observed temperature trends are so much smaller than what models calculate.

3. Is carbon dioxide a pollutant?Lawyers might say, Yes, this is what the Supreme Court ruled in 2007, but scientists are not so sure. A pollutant, by definition, must produce harmful effects. CO2 is a natural constituent of the atmosphere, non-toxic, invisible, having no physiological effects we know ofeven at high concentrations. Its definition as a pollutant relies entirely on its alleged causation of significant global warming and on the additional assumption that a warmer climate is damaging.

(We should take note that CO2 is Natures plant fertilizer. The worlds important crop plants developed when CO2 levels were much greater than todays. Innumerable experiments have demonstrated that higher CO2 concentrations are beneficial for plant growth and therefore benefit global agriculture. Plants not only grow faster, but require less water. All of this is well-known to agricultural experts and to the owners of commercial greenhouses, who often raise CO2 levels artificially to increase productivity. Perhaps we should be grateful to China, the worlds largest emitter of CO2.)

However, before considering CO2 as a criteria pollutant subject to regulation under the Clean Air Act, the Supreme Court ruling requires the EPA to demonstrate by independent research that higher levels of CO2 are damaging to human health and welfare. But the EPAs Endangerment Finding and supporting Technical Support Document (TSD) have been attacked by a large number of plaintiffs. The case was lost before the Court of Appeals of the District of Columbia; it is likely that it will return to the Supreme Court, which may get a chance to modify its 2007 decision.

4. Are we seeing a regime of fear for skeptical climate scientists? Being fairly senior, I am not much affected by the animosity towards skeptics, revealed by the leaked e-mails from Climategate. However, I seem to have lost friends in the academic community and have had considerable difficulty in getting technical papers published in journals whose editors have openly expressed their bias. My real concern is for younger scientists who are just trying to establish their professional careers.

5. Are the views of mainstream climate scientists driven primarily by the desire for financial gain? This is a leading question; I would assume that scientific curiosity is the main driving force. Financial gain may be only one of several additional factors, along with prestige and academic advancement, invitations to important conferences, prizes, etc. However, I would point to the large sums, about $20 billion during the past decade, that the government has spent on climate research, of which only a tiny fraction has gone to skeptics. I also note the multi-million-dollar grants to mainstream climate scientists by private foundations, and even by oil companies such as Exxon and BP. Not surprisingly, the number of scientific publications is roughly proportional to this level of financial support.

6. Is it true that more carbon dioxide and additional warming will be beneficial? Briefly, my answer is yes.

First, Nordhaus correctly states that net benefits (benefits minus costs) should be maximized. This is mathematically equivalent to the well-known result that one should increase pollution control as long as marginal benefits exceed marginal costs. As an expert economist, however, Nordhaus should expand his discussion of more important points:

The discount rate plays a crucial role in the present case, where costs are incurred today, while benefits may be realized 100 years hence. Nordhaus himself uses realistic discount rates of 4%, but he should be more critical of others, like Lord Nicholas Stern, who use discount rates close to zero, which severely skews any cost-benefit analysis by greatly over-estimating the present dollar-value of benefits.

Further, one must ask if there is really any net damage at all from a warmer climate. I wonder why Professor Nordhaus never mentions the work of Yale resource economist Robert Mendelsohn and his 23 economist-colleagues, whose acclaimed book concludes that a modest warming and higher CO2 levels would actually enhance GDP-raising average income, prosperity, and general welfare. True, there are also respected economists who hold a different view; the 1996 report of the IPCC lists results of several of their analyses. While these agree surprisingly well on the total amount of damage, I found that they strongly disagree on individual sectors (like agriculture and others) that make up these totals. And they all assign large economic damage to sea-level riseeven though there is no observational evidence for an influence of short-term (decadal) temperature changes on the rate of rise of sea level.

Finally, it should be obvious, perhaps, but needs to be stated explicitly that if a warmer climate produces positive net benefits rather than damages, then, in principle, one cannot even conduct a cost-benefit analysis. Nor should one try to mitigate emissions of CO2 in any way; our current policies are simply misguided.